The present invention relates to a refrigerating apparatus in which a refrigerant circuit is constituted of compression means, a gas cooler, reducing means and an evaporator to obtain a supercritical pressure on a high pressure side.
Heretofore, in this type of refrigerating apparatus, a refrigerating cycle is constituted of the compression means, the gas cooler, the reducing means and the like, and a refrigerant compressed by the compression means releases heat in the gas cooler, has a pressure thereof reduced by the reducing means, and is then evaporated in the evaporator, to cool ambient air by the evaporation of the refrigerant at this time. In recent years, in this type of refrigerating apparatus, Freon-based refrigerant cannot be used owing to a natural environmental problem and the like. Therefore, an apparatus has been developed in which carbon dioxide as a natural refrigerant is used as an alternative of the Freon-based refrigerant. It is known that the carbon dioxide refrigerant has a very large difference between a high pressure and a low pressure, has a low critical pressure and is compressed to obtain a supercritical state on the high pressure side of the refrigerating cycle (e.g., see Japanese Patent Published No. 7-18602 (Patent Document 1)).
After exiting from a condenser, the above-mentioned Freon refrigerant enters a receiver tank and is once stored in the tank where the refrigerant is subjected to gas-liquid separation. The separated liquid refrigerant is stored in the receiver tank and used for regulation of a refrigerant amount in accordance with an outdoor temperature and the like. On the other hand, in a case where a refrigerant having a supercritical pressure on the high pressure side, for example, carbon dioxide is used, when the outdoor temperature lowers, a saturation cycle is performed, whereby the refrigerant has a gas-liquid mixed state and subjected to the gas-liquid separation in the receiver tank disposed on a low pressure side. The only gas refrigerant is sucked into the compression means. Also in the receiver tank, the amount of the refrigerant to be circulated through the refrigerant circuit can be regulated. However, when the outdoor temperature rises to, for example, +25° C. to +30° C. or higher, the refrigerant is not liquefied, and a gas cycle operation is performed. Therefore, the amount of the refrigerant to be circulated cannot be regulated in the receiver tank, thereby causing a problem that the high pressure side pressure abnormally rises owing to an excess gas refrigerant in the refrigerant circuit.
To solve the problem, a high pressure blocking device is disposed so as to avoid the abnormal rise of the high pressure side pressure, but this high pressure blocking device forcibly stops the compression means to protect a system in a case where the pressure of the refrigerant circuit on the high pressure side reaches a predetermined high pressure blocking set value. However, when the compression means stops, cooling by the evaporator also stops.
Moreover, when oil discharged together with the refrigerant from the compression means circulates together with the refrigerant through the refrigerant circuit, the oil accumulates in a heat exchanger or the like in the refrigerant circuit, and does not easily return to a compressor. Therefore, a refrigerant discharge tube of the compression means is provided with an oil separator to return the oil to the compression means. The oil separator is connected to an oil return circuit provided with an oil cooler, and the oil separated from the refrigerant by the oil separator is cooled by the oil cooler, and then returns to the compression means via the oil return circuit.
Here, in a case where the oil cooler is installed in an air path provided with the gas cooler and these coolers are air-cooled by the same blower, when the outdoor temperature is low, the oil in the oil cooler is excessively cooled, whereby the refrigerant is easily dissolved in the oil. The oil including the refrigerant dissolved therein has a raised viscosity and becomes heavy, thereby causing a problem that a return efficiency to the compression means deteriorates.
Moreover, in the refrigerating apparatus, when the evaporator evaporates the refrigerant to cool an article to be cooled, exhaust heat is generated. Therefore, a system has been developed in which a hot water supply device utilizing the exhaust heat is disposed to achieve energy saving. At this time, the refrigerant before entering the evaporator is allowed to flow into an exhaust heat recovery heat exchanger, thereby performing heat exchange between the refrigerant and a refrigerant of a heat pump unit which generates hot water to be circulated through an exhaust heat recovery medium flow path disposed in the exhaust heat recovery heat exchanger, to generate the hot water by use of the exhaust heat.
Here, when the exhaust heat recovery heat exchanger is disposed on a rear stage side of the gas cooler outside a unit of the refrigerating apparatus, the liquefied refrigerant can be fed to the evaporator, which can improve the efficiency of the refrigerating cycle. However, when the efficiency of the hot water supply by use of the exhaust heat recovery heat exchanger deteriorates, it is necessary to dispose a circuit which bypasses the gas cooler. On the other hand, when the exhaust heat recovery heat exchanger is disposed on a front stage side of the gas cooler, it is not necessary to dispose such a circuit passing by the gas cooler. Moreover, the outdoor temperature has little influence, and hence it is possible to efficiently perform the heat exchange between the refrigerant having a high temperature and water in a water flow path.
On the other hand, in a supercritical refrigerant cycle, on conditions that the temperature of the refrigerant at a gas cooler outlet rises owing to a cause such as a high heat source temperature on a gas cooler side (e.g., a high temperature of outside air which is a heat medium subjected to the heat exchange between the medium and the gas cooler), a specific enthalpy at an evaporator inlet increases, thereby causing a problem that a refrigerating effect remarkably deteriorates. In this case, to acquire a refrigerating ability, the high pressure side pressure needs to be raised, thereby increasing a compression power, to cause a problem that a coefficient of performance also deteriorates.
Therefore, there has been suggested a so-called split cycle (two-stage compression one-stage expansion intermediate refrigerating cycle) refrigerating apparatus in which a refrigerant cooled by a gas cooler is branched into two refrigerant flows, one branched refrigerant flow (a first refrigerant flow) has a pressure thereof reduced by auxiliary reducing means and is then passed through one passage (a first flow path) of an intermediate heat exchanger, and the other refrigerant flow (a second refrigerant flow) is passed through the other flow path (a second flow path) disposed so as to perform heat exchange between the flow path and the first flow path of the intermediate heat exchanger, and is then evaporated by an evaporator via main reducing means.
In the above split cycle apparatus, the first refrigerant flow obtained by branching the refrigerant which has released heat in the gas cooler has the pressure thereof reduced and can be expanded to cool the second refrigerant flow, whereby the specific enthalpy at the evaporator inlet can be decreased. In consequence, refrigerating effect can be improved, and a performance can be enhanced effectively as compared with a conventional apparatus. However, a cooling effect by the first refrigerant flow for cooling the second refrigerant flow before reducing the pressure of the second refrigerant flow depends on the amount of the first and second refrigerant flows passing through the intermediate heat exchanger.
That is, when the amount of the first refrigerant flow is excessively large, the amount of the second refrigerant flow finally evaporated by the evaporator becomes inadequate. Conversely, when the amount of the first refrigerant flow is excessively small, the cooling effect by the first refrigerant flow (i.e., the effect of the split cycle) diminishes.
However, when the exhaust heat recovery heat exchanger is disposed on the front stage side of the gas cooler as described above, there is a problem that control of a valve device on a split cycle side becomes complicated in consideration of control on a hot water supply unit side.